Victor Ovchinnikov

Optical Interference Lithography Using Azobenzene‐Functionalized Polymers for Micro‐ and Nanopatterning of Silicon

Azobenzene-containing polymers (azopolymers) have attracted great interest due to their potential use in various technological applications, including holographic recording, photomechanics, diffractive optics, and microand nanopatterning. [ 1–7 ] These applications are brought about by the effi cient and reversible photoisomerization of the azobenzene moieties between a rodlike trans-state and a bent cis-state, which is accompanied by various changes in the properties of the material system both at molecular and macroscopic levels. [ 7 , 8 ] Remarkably, the photoisomerization can give rise to signifi cant surface mass transport phenomena, allowing one-step inscription of high-quality, thermally stable photoinduced surface patterns onto the azopolymer fi lm. Since its fi rst demonstration in 1995, [ 9 , 10 ] the photoinduced surface-relief grating (SRG) formation has been intensively investigated in various types of azobenzene-containing materials. [ 11–15 ] The phenomenon continually keeps fi nding new potential applications. Recently, the SRGs have been combined with organic solar cells and lasers, [ 16 , 17 ] carbon-based nanomaterials, [ 18 ] and block-copolymer nanostructures. [ 19 ] Furthermore, in recent years, azopolymer-based patterns have been increasingly used as templates for fabricating periodic arrays of, e.g., titanium dioxide, [ 20–22 ] indium tin oxide, [ 23 ] and metallic [ 24 , 25 ]

Processing and recombination lifetime characterization of silicon microstrip detectors

Abstract Three sets of silicon microstrip detectors have been processed and characterized. Recombination lifetimes of each set have been measured by Microwave Photoconductivity Decay ( μ PCD) method. In the this method, the silicon is illuminated by a laser pulse that generates electron hole pairs. The transient of the decaying carrier concentration is monitored by using a microwave signal. The recombination lifetime is a measure of the material quality i.e., defect/impurity concentration which affects the detectors’ electrical properties. A correlation between the recombination lifetime and the leakage current has been observed and discussed. The leakage current density in the best devices was about 6 nA cm −2 at 40 V . The average lifetime in the monitor wafer of this set was about 6500 μs . In comparison, average lifetime less than 1000 μs resulted in leakage currents of more than 100 nA cm −2 .

Fabrication of silicon nanopillars using self-organized gold–chromium mask

Abstract In this paper we present a fabrication process for nanometer scale silicon pillars. High aspect ratio and smooth sidewalls of the pillars are obtained by reactive ion etching of self-organized gold–chromium masked silicon. After annealing, a thin Au/Cr film is converted to the disordered array of metal particles. The particle diameter and density could be controlled by varying the thickness of the films. A set of experiments in fluorine based plasmas has been carried out in order to investigate the processing of silicon quantum pillars. The results show that the mask has a low speed of erosion. Sidewall evolution during low rf power etching has been analyzed. The process parameters for realizing high-anisotropy pillars of different shapes have been found.

Large-area nanostructured substrates for surface enhanced Raman spectroscopy

We demonstrate substantial enhancement of Raman transitions of organic molecules by nanostructured gold-coated substrates at the excitation wavelength of 785 nm and experimentally study the factors that influence the enhancement. The substrates are fabricated by using a robust and cost-effective nanopatterning technique that allows us to create high-density gold- or silver-coated nanopillars simultaneously on the whole surface of a standard silicon wafer.

Focused ion beam lithography for fabrication of suspended nanostructures on highly corrugated surfaces

We propose a nanofabrication method that allows for patterning on extremely corrugated surfaces with micrometer-size features. The technique employs focused ion beam nanopatterning of ion-sensitive inorganic resists formed by atomic layer deposition at low temperature. The nanoscale resolution on corrugated surfaces is ensured by inherently large depth of focus of a focused ion beam system and very uniform resist coating. The utilized TiO₂ and Al₂O₃ resists show high selectivity in deep reactive ion etching and enable the release of suspended nanostructures by dry etching. We demonstrate the great flexibility of the process by fabricating suspended nanostructures on flat surfaces, inclined walls, and on the bottom of deep grooves.

Radiation hardness of Czochralski silicon studied by 10-MeV and 20-MeV protons

We have processed pin-diodes on Czochralski silicon (Cz-Si), standard float zone silicon (Fz-Si), and diffusion oxygenated float zone silicon (DOF) and irradiated them with 10- and 20-MeV protons. Evolutions of depletion voltage and leakage current as a function of irradiation dose were measured. Space charge sign inversion (SCSI) was investigated by an annealing study and verified by transient current technique (TCT). Czochralski silicon was found to be significantly more radiation hard than the other materials.

Luminescence study of silicon nanostructures prepared by ion beam mixing

Abstract Phase separation of SiO x during high temperature annealing results in silicon nanoclusters embedded in SiO 2 matrix. The preparation method which is fully compatible with Si technologies enables independent control of radiation induced damages and stoichiometry of SiO x . The method uses ion beam mixing of a-Si/SiO 2 multilayers by inert gas ions. The nanoclusters show a strong photo- and electroluminescence in the visible and near-infrared region. An excess Si concentration dependent redshift and a luminescence intensity dependence on energy and dose of mixing ions are observed. The role of inert gas atoms accumulated in multilayer film during ion beam mixing is investigated. The obtained results are in good agreement with quantum confinement model.

Fabrication of a silicon based electroluminescent device

Abstract In this paper we present a fabrication process for an electroluminescent device based on silicon nanopillars. The pillars were obtained by means of self-organized gold–chromium mask and reactive ion etching of silicon. Mask properties that influence pillar size distribution can be simply changed by means of thickness of metal layers. The electroluminescent device was made with the help of PMMA (polymethyl methacrylate) layer used for the structure planarization and semitransparent gold layer as electrode. Stable strong electroluminescence in visual and near IR range was observed. This effect was attributed to Si nanocrystallites and ‘hot’ electrons.

Photo and electroluminescence from PECVD grown a-Si:H/SiO2 multilayers

Abstract Multilayers (ML) of a-Si:H/SiO2 have been grown using plasma enhanced chemical vapor deposition. Room-temperature photoluminescence (PL) and electroluminescence (EL) in the range 1.35–1.8 eV has been observed in as-deposited and annealed samples. A noticeable redshift of the PL peak has been detected by increasing the a-Si:H layer thickness in the range 0.7–2.1 nm, as well as the annealing temperature (700–1200°C). The strong correlation between PL and EL spectra indicates that light emission from a-Si:H/SiO2 ML can be attributed to the same luminescence centers in Si layers and nanoclusters. The luminescence mechanism can be interpreted in terms of quantum and spatial confinement of carriers.

Millimetre Wave Phase Shifters Based on a Metal Waveguide with a MEMS-Based High-Impedance Surface

An electronically reconfigurable high-impedance surface (HIS) based on microelectromechanical systems (MEMS) is manufactured and proposed for novel millimetre and submillimetre wave phase shifters. Typically HIS is a capacitive metal grid placed on a dielectric substrate with a ground plane with impedance varying from an initial value to a very high value depending on the frequency of the incident field. Such phase shifters can be developed by introducing a surface with variable impedance in, e.g., a rectangular metal waveguide. In this paper we present design, characterization and measurements of the MEMS-based HIS and of a reflection type phase shifter at 80 GHz